1. Field of the Invention
The present invention relates to cationic polyelectrolytes in powder form, based on acrylamide and quaternised or salified dimethylaminoethyl acrylate, their process of production and their use for the treatment of urban wastes.
2. Description of the Prior Art
Within the domaine of the anti-pollution campaign, the treatment of urban waste waters in purification stations leads to municipal sludges which are advantageously dehydrated preparatory to their dumping or their firing. This dehydration is carried out essentially by filtration or by centrifugation and necssitates the addition to the muds of flocculants, either mineral (aluminum sulfate, ferric chloride), or organic (polyelectrolytes). The mineral flocculants have a certain number of drawbacks, among others: the often incorrect formation of floculate, the low mechanical strength of the floculate rendering these flocculants useless for centrifugation, the maintenance of a residual turbidity, high doses in utilization, etc. Also organic flocculants are more and more preferred, that is to say polyelectrolytes, and more especially high molecular weight water-soluble synthetic polymers. The latter may be nonionic, anionic or cationic. It is generally admitted that the cationic polyelectrolytes are the only ones capable of floculating a mud derived from urban waste waters. Among the cationic polyelectrolytes, the copolymers of acrylamide and of cationic monomers are highly recommended and notably the copolymers of acrylamide and of quaternised or salified aminoalkyl acrylates or methacrylates. In fact, the patent literature supplies numerous formulae of copolymers of this type, but the examples described are very generally limited to copolymers of acrylamide and of quaternised or salified aminoalkyl methacrylates. In fact, it is difficult to find aminoalkyl acrylates commercially. The only one which is proposed is diethylaminoethyl acrylate, and the acrylates generally have the drawback of being much more sensitive to hydrolysis than the methacrylates, whence the difficulties to copolymerise them in aqueous media.
It is an object of the invention to provide improved water-soluble cationic polyelectrolytes in powder form in which the aforementioned drawbacks are minimized.
It is another object of the invention to provide a process for the production of such improved cationic polyelectrolytes.
It is a further object of the invention to provide improved methods of purifying urban muds by means of polyelectrolytes according to the invention.
Other objects and advantages of the invention will emerge from the description which follows.